| Summary: | The performance of symmetric Mach-Zehnder interferometric (<italic>MZI</italic>) sensor employing ring-resonator circuits for slow-light enhancement of the sensor performance was theoretically investigated. The slow-light structures considered in this study are coupled-resonator optical waveguide (<italic>CROW</italic>), four-port single ring-resonator (<italic>FPRR</italic>), and two-port single ring-resonator (<italic>TPRR</italic>) circuits. The performance of the sensors was quantitatively formulated for resolution of refractive index of measurand and figure of merit (<italic>FoM</italic>) with respect to similar <italic>MZI</italic> without employing slow-light structure. The effect of attenuation constant of mode traveling in the ring-resonator to the theoretical ultimate sensor resolution limited by available insertion loss budget was also discussed. Taking realistic ring attenuation constant of 1 dB/cm, ring radius of 300 μm, and 20 dB insertion loss budget, the theoretical ultimate sensing performance using a single-resonator <italic>TPRR</italic> can reach resolution of 3.63E-10 RIU which is 5 times better than single-resonator <italic>FPRR</italic> and 3-resonator <italic>CROW</italic> while giving <italic>FoM</italic> of 5 and 15 times better compared to circuit employing <italic>FPRR</italic> and 3-resonator <italic>CROW</italic>, respectively.
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